Solar cells are widely used to collect solar energy and generate electricity, with multiple solar cells interconnected to form solar panels. There are two main types of solar collectors: silicon and thin-film solar collectors. Silicon is currently the predominant technology, using silicon-based cells encapsulated behind glass. Thin-film processes involve depositing thin-film materials on a substrate to form a light absorbing layer sandwiched between electrical contact layers. The front or top contact is a transparent and conductive layer for current collection and light enhancement, the light absorbing layer is a semiconductor material, and the back contact is a conductive layer to provide electrical current throughout the cell.
In one example of a fabrication process, a metallic back electrical contact layer is deposited on a substrate. A p-type semiconductor layer is then deposited on the back electrical contact layer and an n-type semiconductor layer is deposited on the p-type semiconductor layer to complete a p-n junction. Any suitable semiconductor materials, such as CIGS, CIS, CdTe, CdS, ZnS, ZnO, amorphous silicon, polycrystalline silicon, etc. may be used for these layers. A top transparent electrode layer is then deposited on the p-n junction. This layer may be a conductive oxide or other conductive film and is used for current collection. Once these or other materials have been deposited on the substrate to form a photovoltaic stack, the substrate and thin-film materials deposited may be cut into cells. Multiple cells are then assembled into a thin-film solar panel.
Thin-film solar collectors are lower cost and require lower energy to produce. However, there are numerous sources of defects in a thin-film panel, given the materials used, the large surfaces areas required, the small thicknesses of films, and the sensitivity of the films to small particles. For example, a one micron particle is on the order of the film thickness. Defects from particles and other sources can cause shunts and otherwise compromise solar cell performance.